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What Is a Wait State?

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  • Written By: Mary McMahon
  • Edited By: Nancy Fann-Im
  • Last Modified Date: 21 November 2014
  • Copyright Protected:
    2003-2014
    Conjecture Corporation
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A wait state is a period where the central processing unit (CPU) of a computer cannot operate because it is waiting for something to happen. During this period, the computer slows down, and it can create a bubble, where a glitch in communication delays all commands until the processor can sort it out. This is an especially common problem in a computer with a central processing unit that operates at higher speeds than the memory. The processor must wait for the memory to catch up with certain operations, and can have a lot of lag time as a result.

In a wait state, either the CPU is waiting for a command or has sent a command and is waiting for a result. A common example occurs when a user goes to wake a computer from sleep mode. Instead of immediately starting, it may hang for a moment while the CPU and random access memory (RAM) get back in synch and restart the operating system and any programs that were running when the computer went to sleep.

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A computer with zero wait state does not experience these delays. Commands are instantaneous and the CPU never needs to wait for response from RAM to perform a task. This requires a design where the two operate at similar speeds and the CPU does not have to pause to allow the RAM to synch back up with it. For users, this is preferable as it is more efficient and they do not need to wait while the computer resolves a lag and gets fully operational again.

Some computers naturally induce a wait state. Rather than constantly running the CPU, the computer can shut it off when it is not needed. This reduces the power demand, which can be important for mobile devices. It also keeps the computer cooler and may reduce the need for a cooling system. For a laptop, which can heat up very quickly, a wait state can maintain a safe operating temperature and limit the amount of time the fan needs to run, if at all, which will in turn save energy and preserve battery life.

Computing often develops out of synch, with some components getting faster and more capable while others lag behind. This can enhance the wait state effect, as a computer might have an extremely fast CPU but a slower RAM, and the CPU is limited by the speed of the RAM. Users who are willing to pay a premium may be able to access faster components, if they are available.

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